Have aliens lived on Earth before?

Risingbd Desk: It has been one of the biggest unanswered questions for decades – is there, or was there ever, life elsewhere in the solar system?

Now, a US space scientist believes he may have the answer.

Professor Jason Wright claims that 'technological' aliens may have once lived on one of the planets in our solar system, before disappearing without a trace.

Professor Wright is an associate professor in astronomy and astrophysics at Pennsylvania State University.

In a new paper, titled 'Prior Indigenous Technological Species', Professor Wright suggests that ancient aliens could have lived on either Mars, Venus or even Earth.

And Professor Wright claims that there's a chance we could soon discover 'technosignatures' left behind by the aliens.

In his paper, published in arXiv, he writes: 'A prior indigenous technological species might have arisen on ancient Earth or another body, such as a pre-greenhouse Venus or a wet Mars.'

But most evidence of these aliens would probably be lost by now.

In the case of Venus, the arrival of its global greenhouse and potential resurfacing might have erased all evidence of its existence on the Venusian surface.

And on Earth, erosion and plate tectonics may have erased most such evidence if the species lived here billions of ago.

This leaves just a few places for scientists to look for traces.

Professor Wright wrote: 'Remaining indigenous technosignatures might be expected to be extremely old, limiting the places they might still be found to beneath the surfaces of Mars and the Moon, or in the outer Solar System.'

He believes that the traces are most likely to lie beneath the ground.

He wrote: 'Structures buried beneath surfaces might survive and be discoverable as long as they do not suffer a collision so severe that their artificial nature is obliterated.

'Merely destroying them would render them nonfunctional, but they might still be recognisably technological.

'We might conjecture that settlements or bases on these objects would have been built beneath the surface for a variety of reasons, and so still be discoverable today.'

Professor Wright believes that the growing field of space archaeology could help to reveal clues of the ancient aliens.

He wrote: 'Such discoveries might occur using the tools of the burgeoning field of the archeology of space which includes searching for, finding, and interpreting human artifacts in space.

'Perhaps more likely, imagery and subsurface radar used to study the geology of planetary surfaces might reveal traces of buried structures or other artifacts.'